Plant tissue culture even when started from a single cell can express variations particularly after repeated subcultures, suggesting an emergence of variability; this variation is called somaclonal variation. Somaclonal variation, is not fully understood and possibly comprises chromosome alterations, gene amplification, point mutations, or DNA methylation, may cause changes in crop species (“off-types”), but can also be utilized for selecting useful variants [Larkin P. J. et al.: Theor. Appl. Genet. 60 (1981) 197-214] providing an alternative to the methods of improving agricultural crops by hybridizations or genetic manipulations. Somaclonal variation may, on one hand, enable germplasm improvement without the numerous crossings used in traditional breeding methods, and on the other hand it is not subjected to the public's concern as in cases of genetically modified organisms.
Banana, with an approximate world production of 100 million tons per year, is an important crop plant, although cultivation in tropical regions is complicated by an assortment of parasites comprising viruses, fungi, and nematodes. Since most cultivated varieties of banana are sterile, banana breeding is a slow, complex, and expensive process. Cultivated bananas are natural selections originating from the center of origin of the genus Musa in the Asian Pacific region. The edible types comprise a range of natural hybrids originating from the two species Musa Acuminata (A genome) and Musa Balbisiana (B genome). Most cultivars are triploids (AAA, AAB, or ABB genomes), parthenocarpic and sterile, though in the international trade of dessert bananas, the vast majority belong to the AAA ‘Cavendish’ subgroup. The main focus of banana breeding programs is resistance to diseases and improvements of fruit quality. The extreme susceptibility of the old cultivars to Fusarium wilt (Panama Disease) forced the producers to shift to more resistant varieties. The purpose of this invention is to provide a novel process for selecting banana clones, based on somaclonal variation.
Attempts to utilize somaclonal variation for improving agriculture plants bring usually only modest success, partially due to a very limited control over said variations and due to incomplete knowledge of the mechanisms involved in them, and partially due to niceties of the necessary tissue culture techniques. The exact conditions required to initiate and sustain plant cells in culture, or to regenerate the plant from cultured cells, are very unique for each species and even for each variety. Further, the identification and selection of the improved clones may be quite complex, the differences being evident only at certain stages of clone development [see, e.g., Walther R. et al.: Acta Hort. 447 (1997) 379-86].
Since there is a continuing need of new banana clones, expressing higher yield and better quality of the fruit, it is the objective of this invention to provide a technique—based on somaclonal variation—for selecting banana clones which are characterized by increased bunch weight and fruit yield.
Other objectives and advantages of present invention will appear as description proceeds.